Glass is one of the popular, in-demand materials for different areas of life. It is used in construction and finishing works, works of applied and high art are made from it, and used in the space industry. This is one of the available, simple in composition materials. The most common type that we most often encounter and use products made from is silicate glass.
What is it?
The oldest glass product is considered to be beads found during excavations in Egypt; scientists believe that the find is more than five thousand years old. Since then, the composition of glass has changed little. The main element of the material is quartz sand (Si0 2) - silicate. Soda, potash, limestone and several other elements are added to it.
In industry, to obtain glass mass, oxides of basic substances are mixed and melted in a furnace. The melting point depends on additives that change the properties of glass. The resulting mass is molded in several ways: by making sheet glass, giving it various shapes (dishes, chandelier shades, watch glass, etc.), making blanks for subsequent piece processing by glassblowers, and much more.
Significant contributions to the development of glassmaking were made by Lomonosov M.V., Kitaygorodsky N.I., Mendeleev D.I. and others were interested in the practical side of the issue. It is not difficult to define the material “is silicate? A material having an amorphous-crystalline structure, obtained by melting mixed oxides followed by cooling.
Glass making
The main element for glass production is to which at least five ingredients are added in proportions. Additions are made to the main recipe, depending on the further purposes of using the resulting material: oxidizers, mufflers, decolorizers, dyes, accelerators, and so on. Metal oxides are used as dyes. For example, copper will color a mass of glass red, iron will give a blue or yellow tint, cobalt oxides will give a blue color, and colloidal silver will give a yellow color.
The prepared dry mixture is loaded into where the raw material melts at a temperature of 1200-1600°C, the process takes from 12 to 96 hours. The production of glass is completed by a process of rapid cooling, only under this condition the glass mass will receive all the required qualities: transparency, mechanical resistance and additional properties introduced during the process of mixing oxides.
Types of silicate glass
The production of material is an energy-intensive process, and it is carried out. Glass production in the industry takes place in tunnel-type furnaces with continuous maintenance of a given temperature. The dry mixture is loaded from one end of the furnace, and the finished material is unloaded at the exit.
Due to its widespread use in various industries, silicate glass can be divided into types:
- Quartz without impurities of sodium and potassium oxides is alkali-free glass. It has high resistance to heat and excellent electrical properties. The disadvantage is that it is difficult to process.
- Sodium, potassium, sodium-potassium - alkali glass. The most common type of material, suitable for universal use. It is used to make glass for aquariums, windows, dishes, etc.
- Alkaline with a high content of heavy metal oxides. For example, the addition of lead is necessary to produce crystal and optical glass.
Multi-purpose use
Silicate glass has a number of properties that allow it to be used in a wide range. Each of its qualities can be enhanced, which opens up additional opportunities. For example, glass coated with amalgam serves as a mirror and can also be used as a solar cell under certain conditions.
The hygienic and practical properties of glassware are undeniable. The material is non-porous, which means that pathogenic bacteria do not multiply in it, is easy to clean, and is resistant to any food products. Heat-resistant dishes made from it are multi-tasking: you can bake them at high temperatures in the oven or put them in the freezer without any damage.
Layering and thickness
The material has different thicknesses, which determines its capabilities. Sheet, 2 mm thick, suitable for windows. Aquarium glass is used at least 5 mm, depending on the volume of water poured into the container. However, aquarists are increasingly coming to the conclusion that using an acrylic analogue is much more convenient, especially if a container of 500 liters or more is required.
The use of laminated material (triplex) expands the possibilities: the canvas glued with a polymer film is practically indestructible, it is safe because it does not crumble. It is almost impossible to break two 10 mm thick silicate glasses with a film layer with a hammer. Triplex is used to make transparent bridges, cladding building facades, swimming pool fencing, etc.
Properties
The use of silicate-based materials has its place in construction. They are used not only for making windows, but also as additional protection and a binder. Thus, foundation blocks are treated, which makes them resistant to moisture, fungus, temperature fluctuations, etc.
Bent translucent or matte material is used in everyday life; furniture doors, shower cabins, building facades, and so on are made from it.
Silicate glass has the following properties:
- Transparency.
- Light reflection.
- Environmental friendliness.
- Heat resistance.
- Resistance to aggressive chemical environments.
- Resistance to natural aggressive environment.
- Durability.
- Low thermal conductivity.
Additional qualities, such as resistance to loads and mechanical damage, are imparted to the material by hardening. The essence of the process is rapid heating and equally rapid cooling in a short period of time. Strength increases by 4-5 times. Glass for watches, door panels, furniture, and interior partitions are made from it.
Product manufacturing
Silica glassware and household products are produced in several main ways:
- Pressing. The viscous mass is poured into a stationary mold, after which certain parameters are set using the moving part of the mold (punch). The mold may have a pattern on the inner surface, which is transferred to the outer part of the product during the stamping process.
- Blowing. Differs in mechanical and manual. The wall thickness of the product varies from 1 mm to 10 mm. Vases, bottles, wine glasses, and glasses are made using this method. Hand blowing is an art. Master glassblowers create unique works by combining transparent and colored masses, incorporating metal, natural raw materials, gold, etc. into the body of the work. There are no identical hand-blown products.
- Casting. Mainly used for making figurines and figurines. In industry, they are produced by casting
- Multi-stage articulation. Parts produced using two technologies are used: blowing and pressing. For example, the container of a glass is blown, the stem is pressed, and the finished parts are joined.
Decorative processing
Silicate glass is a beneficial material for many types of decoration. There are hot and cold designs.
Hot ones include:
- Coloring in bulk with metal oxides.
- Mixing masses of different colors with further shaping (Venetian glass with streaks).
- Craqueling. The mass is molded into a product, cooled sharply, as a result of which surface cracks appear, and the product is melted to secure it.
- Fusing.
- Hot molding of cords and threads with subsequent additive to the product.
- Formation of additional edge shape during the blowing process. Achieved by using tools.
Cold forms of decor:
- Mechanical: grinding, engraving, diamond cutting, sandblasting.
- Chemical: etching with hydrofluoric acid.
- Overlays: painting, decal application, silk-screen printing, metallization, plasma spraying, painting with luster paints.
Other types of glass
Modern technologies have made it possible to give silicate glass additional qualities. Of these, the most interesting and popular are:
Smart glass: a type of material that changes its properties under the influence of external conditions. For example, under the influence of electric current, the product becomes matte, but when the circuit is disconnected, it returns to a transparent state.
Fiberglass (fiberglass): are obtained by drawing the material into thin (measured in microns) threads. They create a fairly flexible material. Used for the production of optical fiber, insulating materials, etc.
Clear glass: ordinary silicate glass has a greenish or grayish tint, clearly visible when looking at the cut. As a result, the canvas turns out to be slightly colored. To avoid this effect, brighteners are added during the manufacturing process to neutralize the unwanted color. It differs from conventional material in its increased light transmittance and color transmission without changing color.
Vacu Vin is a brand from the Netherlands, known for its accessories for lovers of wine, beer and cocktails. The Vacu Vin collection also includes glass wine glasses, produced at the Dutch plant Royal Leerdam. Not bad glasses for every day. The price in the Familia store is 799 rubles for a set of 4 glasses for white or red wine. For comparison, the price on the European Amazon is 29 euros. ⠀
Champagne glasses Pasabahce Isabella. Excellent price for the “super sale” promotion in Lenta hypermarkets - 200 rubles for 6 pcs. 33 rubles per glass is slightly more expensive than disposable plastic glasses. An excellent offer ahead of the season of New Year's corporate parties and noisy gatherings with breaking dishes.
N a recent article “Lead and cadmium in cookware: what do suppliers and consumers need to know?” , published on the website posudka.ru, aroused increased interest among readers. Continuing the topic of tableware safety, we decided to assess the scale of the problem and test specific samples from a product group that can be classified as the most risky - tableware with overglaze decals. The test was performed using 3M™ LeadCheck™ swabs, which detect lead in a wide range of materials and are recommended by the U.S. Environmental Protection Agency (EPA). Children's plates were chosen as samples, where the presence of lead is not allowed in principle by current mandatory sanitary standards. The test result showed that consumers have something to fear.
Question:
Good afternoon
Looking for official sales locations for Luminarc cookware in Samara?
Before contacting you, I asked on the Luminarc-Russia website, but they didn’t answer through the feedback form. Then I asked on the Luminarc-France website, through the feedback form - they did not answer. There are no more contacts on both the French and Russian sites. From the Russian site there is a link to the Luminarc online store. On the website of the Luminarc online store there are 2 telephone numbers: Moscow and St. Petersburg. You cannot call these numbers, because you end up in a call center. They don’t know where the official sales points for Luminarc cookware are in Samara (they say they don’t buy stores from Samara). They also don’t know the phone numbers of Luminarc representatives.
This secrecy of the dishware company is alarming. Or is this normal? It seems that the company itself should, on the contrary, post verified addresses on the website.
Please tell me where are the official sales points for Luminarc cookware in Samara? Or how to contact Luminarc representatives (who can answer this question)?
If you don’t know any stores or representatives, how can you identify real dishes or crafts?
Which factory (in France, China, UAE, USA and Russia) a particular cookware was made should be written on the sticker label? Or is France written everywhere?
Do Luminarc plates, salad bowls, cups, mugs withstand temperature changes? That is, if in winter (when the dishes are a little cool) you pour freshly boiled water into a cup; If you pour freshly cooked soup into a plate or put a freshly prepared second dish, will the dishes withstand these changes? Over time (for example after 3 years) will Luminarc cookware also withstand temperature changes?
The decal of Luminarc tableware is underglaze in all collections?
Can children eat from non-children's Luminarc cookware? You mean, do the children's and non-children's series differ in quality or only in design? What class of Luminarc cookware (cheap, average...)? Are there brands of glassware that are superior in quality to Luminarc (as an alternative)? Where can I buy in Samara?
Denis, Samara
Answer:
In Samara, Luminarc dishes can be purchased in almost any hypermarket; among specialized stores, we can recommend the Posuda Center chain (this company is one of the distributors of Arc International). There is no need to worry too much about Luminarc fakes - they practically never occur.
Information about the country of origin can be found on the packaging or on a sticker on the product; the information provided is real.
Luminarc dinnerware is not heat resistant in the sense that it cannot be used in the oven. But you can pour hot drinks and dishes into it without any problems. Luminarc glassware can also be used in the microwave for heating. Just don’t cool hot dishes instantly - there is a risk of destruction. Temperature resistance does not depend on service life.
There is no underglaze decal on glassware, because... no glaze itself. The decal can be applied either to the inner surface of the dish (which is in contact with food) or to the outer surface (in this case it is visible through transparent glass). Luminarc children's cookware lines are produced using the second technology.
It is difficult to give a definite answer about the Luminarc class of cookware. On the one hand, it is more expensive than glassware from other brands of Chinese or Russian production, on the other hand, glass itself is an inexpensive material, and glassware of even very high quality is often cheaper than even average porcelain tableware.
For alternatives to glassware, you can look at another Arc International brand - Arcoroc glassware made from a material called Zenix. This cookware has increased mechanical strength and a presentable appearance.
Question:
Hello!
I bought plates at the OK hypermarket that cost 109 rubles, diameter 19 cm. It is written on the sticker on the outside that they are made of glass and made in the UAE, manufactured by ARC INTERNATIONAL MIDDLE EAST, and on the inside there is a sticker with the inscription Luminarс, supplier importer LLC "Company" Arch".
I didn’t find such a company among official suppliers. The outside of the plates are covered with color, the inside looks like glass, heavy. I want to buy all sizes.
The question is, can they be put in the microwave and washed in the dishwasher? Because There are no signs other than the PCT. And isn’t Luminarc from France, did I buy a fake?
Elena, Moscow
Answer:
Apparently, we are talking about the Luminarc Colorama series of cookware. It, like other Luminarc glassware, can be used without problems in the dishwasher and microwave. Regarding the country of production, the Luminarc trademark belongs to the French concern Arc International, which has its own production facilities in different countries: France, China, the UAE, the USA and Russia (dishes under the Luminarc brand, in particular, are produced by our Experimental Glass Factory). The quality of the products, regardless of the country of origin, is quite high.
Question:
Hello, please tell me how to store cooked milk and dairy-free porridges in the refrigerator (we cook them in stainless steel containers). And is it possible to store prepared meals in non-stick cookware? Is it possible to store only milk in ferritic steel containers? And the second part. Question: Is it true that dishes imported from China (both steel and especially ceramic, for example, pots for baking in the oven) often carry a radiation hazard and are turned away at customs?
And another question: they sell colored glass tableware (they gave us a light green one), from a manufacturer like the Russian Federation. Is this material safe?
Ksenia, Samara\
Answer:
Utensils made of glass, enameled steel, ceramics, and porcelain are well suited for storing any cooked food. Cookware with a non-stick coating is less suitable for storage, but if you leave cooked food in it for a day or two, nothing bad will happen. It is not recommended to store food in ferritic steel dishes, as the color and taste of the food may change.
When crossing the customs border, all goods undergo radiation control. Ceramic dishes in large quantities (for example, a full 20- or 40-foot sea container) can trigger the sensor (small batches of ceramic or porcelain dishes do not produce background radiation). After this, samples of dishes are usually sent for additional control, which determines whether the background radiation is within the normal range or not. Most often the issue is resolved positively. In addition to porcelain tableware, other ceramic products, such as ceramic tiles, have similar problems with radiation monitoring. The country of origin does not really matter here; goods are simply imported from China in larger quantities and in larger quantities.
Russian-made glassware will be safe to use. Colored glass plates are made by a factory in Bor, Nizhny Novgorod region, under the Pasabahce brand.
Question:
Hello! I have long been in love with Pasabahce dishes. The assortment is wide, from different series of dishes you can create an entire service, at a budget price. Everywhere there is information that this dish is made of tempered sodium-calcium silicate glass. Tell me why the manufacturer emphasizes this? Does this glass have any special properties compared to “regular” glass or is it just a marketing ploy? And I also noticed that their glass always has some small defects that may not even be immediately visible - scratches, marks and other “manufacturing marks”. Therefore, I always take a closer look and try to choose a copy that, from my point of view, is of higher quality. The sellers say that this is not a defect. I would like to hear your opinion: is this still a defect or is this glassware simply not of high quality glass? And what kind of glass is this anyway?
I would like to express my gratitude for your attentive attitude to our questions!
Ekaterina, Orsk
Answer:
Sodium-lime silicate glass is an inexpensive material related to ordinary glass. Budget dishes are usually made from it. Hardening increases the cookware's resistance to mechanical stress.
Sagging, bubbles, scratches and other minor defects are very common on inexpensive cookware; according to GOST, a small number of defects are allowed, so in most cases this really cannot be called a defect.
Question:
Hello! Please recommend high-quality cutlery (knives, forks, spoons) and glasses.
Julia, Belgorod
Answer:
High-quality cutlery is easy to distinguish visually - they are quite massive, the edges and edges of the cutlery (especially forks) are well polished and do not have defects - burrs, sharp edges. Before buying, it is also advisable to hold them in your hand - they should be comfortable. Among the brands we can recommend Pintinox, ROBERT WELCH, Cutipol, Paderno, Sambonet, etc.
The choice of glass glasses is also quite simple; visually, all the advantages and disadvantages of glass are clearly visible. Good glasses are made by hand blowing - they are light, thin and elegant, the edge has no rim, the walls of the glasses, when exposed to light, are smooth, transparent and without defects (bubbles, layers, unevenness). Hand-blown glass is quite expensive, so for everyday use it is quite possible to use stamped glasses. Quality here is also determined visually - the glass must be as transparent as possible and free from defects. Among more expensive products, we can recommend glasses from the brands Riedel, Schott Zwiesel, Spiegelau, Rona, Leonardo, etc. For stamped glasses, you can see something from the Arc International or Royal Leerdam range.
When choosing both cutlery and glass glasses, if you do not have much experience, you can proceed as follows - first look and hold in your hands several samples of premium products, so that you have an idea of what quality products look like, and then look at more affordable ones products, focusing on their own “like-dislike” feelings.
Glass- a material with an amorphous-crystalline structure obtained by supercooling a melt consisting of oxides of various metals.
Crystal- This is a type of simple glass (you need to add lead to the glass).
Common glasses include
potassium – calcium – silicate glass
The main difference between crystal and glass– addition of lead oxide during manufacturing – from 6 to 36% (world standard – 24).
Key quality indicators.
Destination indicators– linear dimensions and capacity of products, stability on a flat surface, density (for crystal). Reliability indicators– quality of annealing, heat resistance, water resistance, strength of parts fastening.
Indicators of aesthetic properties– they are standardized through the conformity of products to the standard sample and the care of manufacturing. For crystal glassware, optical properties are regulated - refractive index, transparency.
Classification of glass products for household use. Decoration methods.
Depending on the type of glass, household products are divided into products made from ordinary glass, crystal and special glass.
Common glasses include
sodium – calcium – silicate(Produces household utensils (cans, bottles) and cheap, usually colorless, everyday tableware from this glass. cheap) and potassium – calcium – silicate glass (This glass is somewhat more expensive; it is used mainly for the production of tableware.).
A group of crystals unites the glass, which contain lead oxides. Lead oxide helps increase the density of glass, improves optical properties: transparency, “whiteness” (colorlessness), and increases the refractive index (brilliance, sparkle).
The third group - special glasses - is represented by borosilicate heat-resistant glass and glass-forming materials - glass ceramics. These glasses are characterized by increased heat resistance and mechanical strength (primarily characteristic of glass ceramics). Borosilicate glasses can withstand heating up to 500C, are resistant to thermal shock, which determines their use in the production of kitchen utensils: pots, braziers, frying pans, baking dishes, etc. Sitalls – glass-like materials with a crystalline structure, maximum mechanical strength (tens of times greater than ordinary glass), and high heat resistance. These materials are characterized by low transparency and are most often white in color. .
Depending on the type of jewelry there are different products with decorations applied during the formation process, as well as on finished products. Decorations applied during the formation process include: coloring in the mass, color, optical pattern, decoration with a roller, colored spots, crackle, decoration in bulk (crumbs), decoration with glass threads, etc. Decorations applied to finished products divided into three subgroups:
1 .mechanical methods of decoration (grinding, engraving, diamond cutting, sandblasting waterjet processing (usually through a stencil).
2. chemical decorations (guilloche, pantograph and deep artistic etching).
3. applied (surface) film decorations (painting, decal, silk-screen printing, stencil, metallization, iridescence, plasma spraying, decoration with luster paints).
42. Examination of textile materials by fiber composition: methods and procedure.
Cotton, linen and woolen fabrics are produced in the 1st and 2nd grades, silk - in the 1st, 2nd, and 3rd grades. In this case, the type of fabric is determined in accordance with GOST standards for fabric. By examining fabrics from the front side on specially equipped tables, defects are identified, which are divided into acceptable and unacceptable, local and widespread. The general indicators by which the type of fabric is determined are the number and size of defects in appearance and deviations in physical and mechanical parameters. Defects in appearance include defects in yarn (knots), weaving (thread breaks) and finishing. Unacceptable defects are subject to a cut, which is made across the entire width of the fabric along the line where the defect is located, or a cut at the location of the defect, the size of which does not exceed 3 cm. Non-woven materials are classified into grades 1 and 2. The grade is determined depending on defects in appearance and deviations in physical and mechanical indicators, which are assessed using a point system. All defects are divided into local and widespread. Locals recalculate to a conventional area. Local ones include: oil threads, knots, broken stitching thread; Common ones: dead hair, lack of coloring, pattern failure, different shades.
The range of glass products is quite dynamic and changes due to the constant development of science, the state of production technology, the nature of consumer demand, and changes in style trends.
The range of household products is classified according to purpose and operating conditions, composition and color of glass, molding method and nature of heat treatment, types (names), sizes, styles of products, methods and complexity of decoration, and completeness.
According to their purpose, household goods are divided into dishes and decorative items for table setting and interior decoration, household utensils for food storage and home canning, kitchen utensils for cooking, lamp products (table lamps, lamp tanks, lamp glasses) and mirrors.
According to the composition of the glass, dishes are distinguished from sodium - calcium - silicate, special household and crystal glass.
Tableware is made from sodium-calcium-silicate glass, various types of crystal, as well as tempered borosilicate glass; household utensils - made of sodium-calcium-silicate glass with additives that increase chemical and thermal stability; kitchen - from special household glass and ceramic glass.
Based on color, glassware can be distinguished from clear glass, colored glass (painted in the mass) and surface glass (two layers). The names of colored glasses are given according to the color tone (yellow, green, pink, etc.), according to the nature of the dye (cobalt, manganese), by analogy with precious stones: rubies (red), topazes (yellowish-brown), sapphires (light -blue), emeralds (light green).
According to the molding method, dishes are distinguished between hand-blown, free-blown, machine-blown, pressed, press-blown, multi-stage molded, bent, and centrifugally made.
According to the method of heat treatment, a distinction is made between cookware that is not hardened, i.e., annealed, and hardened by hardening.
The overwhelming majority of products made from grade glass and all crystal products are produced annealed.
Hardening consists of heating products to 700 °C and subsequent rapid and uniform cooling by blowing air. At the same time, high, evenly distributed residual stresses arise in the glass, increasing the impact strength by 5 - 8 times, and heat resistance by 2 - 3 times. Some types of pressed tableware and kitchenware made from heat-resistant borosilicate glass are strengthened by tempering.
Types of glassware
There are about thirty types of tableware; These are glasses, goblets, shot glasses, goblets, wine glasses, jugs, decanters, sugar bowls, oil dishes, vases for table setting (for fruit, jam, cookies, cream, sweets, salad bowls), mennazhniki, etc.
Decorative items include glass sculpture, flower vases, toiletries, horn-shaped glasses, dishes, etc.
Each type of product is produced in several varieties (articles), differing in size and style.
By size, dishes are divided into small, medium, large, and extra large. The size of products is characterized by diameter, length or height, and the size of hollow products is characterized by capacity.
By style, products are subdivided taking into account the shape of the body (ball, oval, cone, etc.), the presence of stick-on (handle, leg, lid holder) and removable (cork, lid) parts, the nature of the edge (smooth, cut-out) and the bottom of the products. The dishes are produced with a bottom of regular thickness, thickened, and also on a pallet (a protrusion or ledge at the bottom of the product).
The legs of products can be of different heights, shapes (straight or figured) and processing (faceted and smooth). Blown flower vases are divided into three groups depending on the complexity of the shape.
The style, along with the aesthetic features of the glass melt and cutting, largely determines the artistic expressiveness of the products. It is subject to change according to style requirements. Currently, festive and giftware is distinguished by a complex silhouette, careful processing and complex shape of parts. Everyday utensils have simpler and more solid shapes.
Based on the method of decoration, a distinction is made between smooth and decorated dishes. Decorated dishes, depending on the nature, complexity and artistic merits of the cuts, are divided into group and non-group. Cuttings of group blown glassware from varietal colorless glass are divided into groups 1-7, from colored glass - into 3-8th, from applied glass - into groups 4-8. Cutting crystal products belongs to the 4th-10th difficulty groups.
The group combines drawings of the same complexity, but with different plots. They are designated by three-digit numbers in which the hundreds digit indicates the group number.
Out-of-group products are characterized by original forms, complex, often combined designs of high artistic value. They are individual for the products of each plant. Many products with the “H” index and sold at negotiated prices are classified as non-group products.
The cutting of pressed products is not divided into complexity groups.
Modern trends in the decoration of glassware - expansion of the range of colored glass, a combination of colored and slightly muted glass in the overlay, contrasting combinations in the design of elements of a diamond edge, matte engraving, chandelier, widespread use of decal patterns and silk-screen printing of various subjects, picturesque cuts with paints and gold, often in combination with matting. Thin cuts and products are still popular.
Based on their completeness, they distinguish between piece products, sets (including products of the same type - a set of glasses, etc.), cutlery (containing products of different types for the same purpose) - for water, jam, cups, toiletries, etc. The products of the sets are characterized by the unity of artistic and constructive solutions.
The range of tableware for table setting is extremely diverse and is grouped taking into account all the previously mentioned characteristics. Main types of products: glasses, mugs, cups, goblets, wine glasses, shot glasses, goblets, decanters, jugs, milk jugs, vases for table setting (for fruit, cookies, sweets, jam, cream, salad, bread bowls), butter dishes, sugar bowls, rusk bowls etc.
Decorative items are represented by sculptures, flower vases, toiletries, horn-shaped glasses, etc.
Household utensils are produced manually or mechanically from colorless and semi-white glass. The range includes thermoses and other products for storing food - jars, jars for pickles and jam, kegs, bottles for storing liquids. Thermoses are divided according to their purpose into thermoses for liquids and food (with a wide neck), according to the capacity of the flask, design and shell material (metal, plastic, combined).
Kitchenware made of heat-resistant glass and glass ceramics is represented by pots of various capacities, baking dishes, braziers, and frying pans. Sets of pots and the “Baby” set are produced from glass ceramics. Heat-resistant glassware is tempered and not decorated. White glassware with a smooth shiny surface is additionally decorated with decal patterns.
- October 27, 2015 Guest (nastya)
www.treeland.ru
What utensils are harmful to health: what you can and cannot cook food in
Can dishes be harmful to health: what should you store and cook food in?
To avoid many diseases, it is important not only to eat right, but also to know which dishes are harmful to health, because the material from which they are made can release hazardous substances.
Is there such a thing as safe utensils for health?
Among the wide range of products for storing and preparing food, cast iron, clay, enamel cookware and those made of stainless steel are considered safe. In all other cases, harmful utensils can have a negative effect on the human body:
- Release toxic substances when heated;
- Cause severe allergies or food poisoning;
- Oxidize, resulting in the activation of harmful substances.
Of course, when choosing any cookware, you should pay attention not only to the material from which it is made, but also to the composition, which is usually indicated on the labels. For example, low-quality stainless steel may contain nickel, which gives food a metallic taste when heated.
What kind of dishes can and cannot be used to cook food ^
Dishes harmful to health: myth or reality
Cast iron cookware: benefits and harms
Products made of cast iron are best used for frying or cooking, because food does not burn in it, and the material itself is environmentally friendly and becomes stronger and safer over time.
Aluminum cookware: harm and benefit
It is precisely such dishes that are considered the most harmful, because when heated they actively release metal ions. Under the influence of acids contained in milk or any other product, aluminum passes into food.
- It is strictly forbidden to fry or cook soups or vegetables in such pans.
- Daily use of aluminum utensils often leads to food poisoning.
Copper utensils: benefits and harms
Utensils made of copper are completely harmless to the body, because even if its ions enter it, they are eliminated very quickly.
- Despite this, it has a significant drawback: when preparing fruits or vegetables, copper destroys most of the vitamins they contain;
- If food contains acids, it can react with them.
Harm of crystal glassware
Most often, people drink drinks from crystal glassware, in which case it is considered safe.
- If liquids are stored in it, it begins to release lead, which subsequently causes harm to the body.
Silicone cookware: benefits and harms
Despite the fact that silicone contains chromium, cobalt, copper and other components, bakeware made from it can be safely used:
- Thanks to the special technologies and requirements for the production of such utensils, the release of harmful substances under the influence of temperatures does not occur.
Enameled cookware: benefits and harms
Initially, enamel cookware was designed specifically to protect against metal ions getting into food, but here it all depends on the color of the coating:
- Blue, black, cream, white or blue-gray color is considered safe,
- You should avoid red, yellow or brown shades - they contain a lot of dyes and have low protective properties.
Silverware: benefits and harms
Since ancient times, dishes made from silver have been considered the best: they not only look good, but also kill all kinds of bacteria, thereby preventing them from entering the human body.
- More recently, some media reported that this metal is not able to retain useful elements and remove harmful ones, but there is no direct evidence of this.
Why are utensils made from polypropylene harmful?
Plastic dishes have three degrees of heat resistance:
- high,
- average,
- low.
In the first case, we mean containers for food that can be placed in the microwave, and in all the others, we mean all kinds of bowls, cups, forks, spoons, etc. Regardless of the ability to withstand high temperatures, heating food in such containers is not recommended, because at high temperatures the plastic can melt and release harmful elements.
Polypropylene dishes should also not be used for storing food.
Stainless steel cookware (stainless steel): harm and benefit
Steel cookware can be safely used for frying and preparing entrees, but you should not store food in it because it can release nickel, which can leach into your food.
Cupronickel tableware
For several centuries, products made from cupronickel have been very popular, and for good reason: despite the fact that they are made from an alloy of copper and nickel, they are safe for human health - you just need to clean them from plaque in time.
Pewter
In general, utensils made of tin are safe, but if they contain lead impurities, which cause them to darken over time, it is best not to use them.
Glass ceramic dishes
Dishes made from ceramics are harmless only if there are no chips or cracks on them, otherwise heavy metal salts may enter the body.
- In addition, the inside of plates made of such material may contain designs made with paints containing lead, so it is not recommended for its intended use.
Galvanized cookware
- Such utensils are not suitable for heat treatment of products, because... when heated, it releases zinc.
- You should not store food in it for the same reasons.
Teflon coated cookware
Nowadays, not only frying pans, but also other kitchen utensils are coated with Teflon, but if the integrity of the coating is damaged, it is best to get rid of such utensils, because they provoke the development of obesity and cancer.
Melamine tableware
- If such dishes are damaged, they begin to release a dangerous poison - formaldehyde.
- In this case, it must be abandoned. It is also not suitable for frying or boiling.
Ceramic cookware: harm and benefit
- Unlike Teflon, thermolon-coated utensils are more harmless because... its negative impact on human health has not been confirmed.
- In addition, it can be heated to 400 degrees or more.
Glassware: harm or benefit
Like ceramic containers, glass casserole containers, mugs and plates do not cause any harm to health, because they are made without the use of elements that negatively affect the human body.
Acrylic tableware
- If you do not heat food in such utensils, then it is quite safe.
- Unlike harmful disposable tableware, it can be used repeatedly, and in this it obviously wins.
Opal tableware: harm and benefit
Thanks to modern technologies, opal glassware turns out to be very light and elegant:
- Various designs can be applied to it, which does not affect its strength in any way.
- It has virtually no pores, which allows it to be considered completely safe for storing food.
- Tolerates temperature changes well, from high to low. Pans made of frosted glass are perfect for use in microwave ovens.
- It has low thermal conductivity, which allows you to keep food hot for a long time.
- It is easy to wash and is easy to keep perfectly clean.
- Resistant to the use of any detergents, they do not cause visible harm to it.
- Having increased durability, these dishes can be stored in stacks, which saves space in your kitchen.
Which dishes are not harmful to health?
Nickel-plated cookware is considered the most harmful, because... it contains nickel, however it is the most common. It is best to prepare and store food in containers made from the following materials:
- Clay;
- Cast iron;
- Stainless steel (you can’t leave dishes in it for a long time).
Harm from plastic bottles and plastic film: what is the danger ^
Plastic containers may contain the chemical substance bisphenol-A, a synthetic analogue of the female sex hormone, which can penetrate into water or liquid, and then into the human body.
If you drink water from plastic bottles, you increase the content of bisphenol in your body:
- Scientists at Harvard University conducted a study and found that drinking cold plastic liquids for just one week increases the level of bisphenol in urine by 69%.
- The release of bisphenol depends on temperature. The higher the temperature, the more active water pollution occurs with bisphenol from plastic. That is, ordinary summer heat can increase the concentration of harmful substances in water tenfold.
- If you fill plastic bottles with hot liquid or specially heat them, the release of bisphenol will increase up to 55 times! This fact should be known to parents who heat milk in plastic bottles for their children.
- Increased concentrations of bisphenol increase the likelihood of prostate cancer in men and have a negative impact on men's health, as hormonal levels are disrupted.
- Pregnant women are generally contraindicated to drink water from plastic bottles, since due to bisphenol poisoning, the child may be born with birth defects.
happy-womens.com
Carefully! Harmful dishes
We all periodically prepare food for ourselves and our loved ones. We eat several times a day. Do we know what exactly we cook with and what we eat from? Do we use healthy or harmful utensils? Let's figure it out.
In Rus', dishes were traditionally made of wood. Moreover, not every tree was suitable for its manufacture. The healing properties of wood were of great importance.
Thus, it was believed that dishes made from linden had anti-inflammatory properties, while those made from rowan protected against vitamin deficiency. It is known that birch bark has many medicinal properties - from bactericidal to tonic. They ate with wooden spoons from wooden bowls, and used wooden bowls, ladles and jugs. In addition, they wove dishes from birch bark - salt shakers, tueski for storing flour and cereals.
Copper utensils appeared next. Perhaps you also have a copper basin or saucepan in your kitchen? Indeed, in many families, dishes made of copper and its alloys are passed down from generation to generation. And no wonder: they always used it with pleasure! The fact is that, due to its high thermal conductivity, copper has a remarkable quality for cooking - heat is evenly distributed over the surface of the cookware. And therefore, delicious jam, aromatic coffee or a wonderful sauce are obtained in copper dishes as if by themselves.
But modern science somewhat darkens our emotions - it warns: even a very small amount of this metal destroys ascorbic acid in berries and fruits.
And one more thing: food stored in copper dishes loses vitamins, polyunsaturated fatty acids in it are easily oxidized, forming compounds dangerous to the body - free radicals.
With its frequent use, poisoning is possible.
In addition, copper in a humid environment easily oxidizes and a green or blue-green film appears on the dishes - patina. When heated, it interacts with food acids, forming copper salts that are harmful to the body.
Therefore, after washing, the plate or basin must be thoroughly wiped, avoiding the formation of a film. If, however, patina does appear, then it must be carefully removed from the entire surface, otherwise using harmful utensils will be dangerous to health. You can do this this way: wipe with table salt soaked in vinegar, and immediately rinse first with warm, then with cold water.
Lead in ceramic dishes
For centuries, lead was added to the alloys from which dishes were made. The sad consequences of this are now well known to scientists: lead, gradually accumulating in the human body, led to poisoning.
In the Roman Empire, wine vessels and other kitchen utensils contained large amounts of lead. As a result of the use of such harmful utensils, the life expectancy of the population has decreased by almost half. Some historians even believe that lead poisoning of the Roman “elite” was not the last reason for the decline of the powerful state.
Also in our time, scientists have proven that lead is guilty of destroying the health of the Moscow princes - the water that was supplied to the Kremlin flowed through a lead water supply system...
In many countries around the world, more than a quarter of a century ago, a ban was introduced on the use of lead in the production of tableware.
But despite this, even today you can easily become the owner of harmful pots or, for example, cups.
Here it is appropriate to recall the well-known story of an American couple.
Once, while vacationing in Italy, the couple bought beautiful ceramic cups. When they arrived home, they did not put them behind glass in the cupboard to admire and show to guests, but began to actively use them every day.
After two and a half years, both spouses began to show signs of lead poisoning: insomnia, nervous disorders, sudden attacks of pain “walking” through different parts of the body. The doctors to whom the sufferers turned were at a loss - they could not understand what was the matter.
The man even underwent two completely unnecessary surgeries, and the woman was persistently treated for liver disease.
But, following the well-known saying “saving drowning people is the work of the drowning people themselves,” the American couple, having “shoveled” a mountain of special medical (and maybe not only) literature, diagnosed themselves with lead poisoning! And he was absolutely correct, which was later confirmed by specialists working with poisons.
Let's try to figure out how lead got into the dishes (after all, the cups are ceramic, not metal!). Most likely, they were decorative, which means they were not intended to be used for drinking tea, coffee and other drinks.
The fact is that according to sanitary standards, the presence of lead in the manufacture of decorative dishes is allowed. It turns out that it is added to paints to give pottery smoothness and a beautiful shine. But: the instructions for using such products must clearly state that food cannot be stored in them! And we must understand that this is harmful utensils.
Therefore, we draw a conclusion for ourselves: if we buy a brightly colored plate, cup, or pot that we like, don’t be shy and be sure to ask the seller for a certificate. And in this document we are looking for information about the results of testing dishes for toxic substances. But, unfortunately, the reality is that certificates are often counterfeited.
So, maybe it’s better to be careful and not buy ceramic products with too bright red and yellow painting, which almost always indicates the presence of lead and cadmium in the paint.
By the way, the bright green color may be “tinted” with copper. And it, in addition to being not useful in itself, also accelerates the process of lead release. Therefore, it is not forbidden to purchase such cups and plates for beauty, but for everyday use for their intended purpose, experts categorically do not recommend them.
Lead in cans
In addition to harmful dishes, some cans can also become a source of lead poisoning, since their elements are connected to each other with solder containing lead. Such cans are easily distinguished by their corrugated seam and silver-gray connecting line with irregular outlines. Although the inner surface of the cans is usually coated with a special compound, this does not always help.
There are known cases where, during long-term storage, lead accumulated up to 3 mg/kg, which is much higher than the permissible level. Its content can be especially high in canned acidic foods: tomatoes, fruit juices, etc.
In addition, they usually contain another toxin - tin.
In order not to expose yourself to danger, you should buy canned food in tin cans with smooth welds that are located between the sticker and the upper or lower end of the can.
Aluminum
Aluminum cookware could be seen in almost every kitchen 10-15 years ago. It is easy to clean, and food does not burn in it when cooking. It’s very good to boil milk in such a saucepan, cook milk porridges, jelly, vegetables for vinaigrette and salad, etc. But, sadly, all this food turns out to be “flavored” with aluminum!
Both under the influence of milk, as a representative of alkali, and under the influence of the acidic environment of vegetables being cooked in microscopic doses, aluminum “peels off” from the dishes and safely ends up in our stomach. Aluminum does not oxidize in water, but even it “washes out” its microparticles.
So you should neither boil water nor store it in harmful aluminum containers, just like any other products.
No, if you cooked rolled oats porridge for your child in an aluminum ladle once or twice, nothing bad will happen. But if you do this every day, then don’t be surprised that the baby has become terribly excitable.
Well, if you cook for yourself in dishes made of this metal for years, then the opinion of experts is this: sooner or later enough aluminum will accumulate in your body to provoke such serious diseases as anemia, kidney disease, liver disease, various neurological changes and even Parkinson’s disease and Alzheimer's disease.
Relatively recently, beautiful melamine dishes made in China and Turkey appeared in our kitchens. In appearance it resembles porcelain, but is much lighter in weight. Due to its very attractive appearance and purity of colors, it is popular among buyers.
But these are toxic and harmful dishes! One of the sources of danger is salts of lead (again!), cadmium and other metals that are part of the paints with which she paints.
Paints applied using the decal method are not coated with any protective layer, and they very easily get into the products.
Another danger is that melamine contains toxic formaldehyde. It is emitted by many plastics, but melanin, according to the results of special studies, does this especially strongly - tens or even hundreds of times exceeding the permissible norm. In experimental animals, such doses of formaldehyde cause mutagenic changes in the body and the formation of cancer cells.
The sanitary and epidemiological inspection banned the sale of melamine tableware. But go to the tableware department at any market and you will see cute cups, plates and all kinds of sets of them.
In addition to melamine, you can also find harmful dishes made from other polymer metals on sale.
Specialists involved in testing and certification of this product believe that it can be used, but only with strict adherence to the manufacturer’s instructions.
For example, if plastic containers are intended only for bulk products, then liquids cannot be kept in them, otherwise they may absorb toxic substances. If the instructions for using, for example, plastic containers say that they are for cold food, then there is no need to put hot food in it, etc.
"Stainless steel" and silver
Recently, utensils made of stainless steel - an alloy of iron, carbon and other elements - have become very popular. Steel with additions of 18% chromium and 8% nickel is widely used for the manufacture of kitchen utensils. If it is made of high-quality steel (and the production technology is not violated), it does not change the taste of the products and is safe for health.
Pots and pans made of this steel are preferable with a thick bottom - they provide gradual heating and prolonged cooling. Stainless steel cookware should not be overheated - after this the food in it will burn. And one more thing: we must remember that nickel is a strong allergen, so people with allergies should be careful with it.
Enamel and glass
Perhaps, good old enamel cookware meets all safety requirements. It is, of course, in every home. Its main advantage is enamel, which, due to the inertness of its components, does not interact with salts, acids, or alkalis. This is what makes enamel utensils very popular.
Of course, such dishes can only be used intact. After all, in places of damage, cracks and chips, yellowish-red spots appear that are not removed by washing. This is ordinary rust. And it, interacting with food acids, forms iron salts that are harmful to humans. In addition, when washing, particles of the cleaning substance may remain in the damaged areas, which will also then enter your stomach.
Another type of safe cookware is made from heat-resistant glass. To give glass these properties, elements are added to its composition that retain strength at high temperatures. So there is no need to be afraid that a teapot made of such glass on a gas fire or a baking tray in the oven may crack, crumble, etc.
But we must remember that when using heat-resistant cookware, when it is in a “hot state”, you must avoid its contact with very cold surfaces - then the pan will burst.
Glass is also chemically inert, like enamel, so dishes made from it are not dangerous from this point of view. In addition, it is convenient - it washes well and the food looks beautiful in it both when cooking and when serving.
This begs the question: is there such a thing as completely safe cookware? Maybe it's best to eat from a silver plate with a silver spoon and drink from a silver cup? After all, everyone has heard about the healing properties of this metal and the history of Suvorov’s army, where officers did not suffer from gastrointestinal diseases, since they ate from silver dishes, while soldiers in large numbers died from these diseases?
Indeed, experts say, silver ions suppress the development of pathogenic microflora in aqueous solutions.
But it turns out that food enriched with silver ions, when consumed for a long time, can adversely affect the human nervous system, cause headaches, a feeling of heaviness in the legs, and weaken vision. And if, again, you use silver utensils constantly, for years, you can “earn” such a serious disease as gastroenteritis and even cirrhosis of the liver!
Teflon is the trade name for a polymer used for non-stick coating on cookware. Indeed, food will not burn on a Teflon frying pan, even if we lubricate its surface with only a minimal amount of oil or fat. Agree, this will benefit our health, right? And we don’t need excess fat, or any harmful carcinogenic substances that are formed when food is overcooked, especially.
But in order for Teflon cookware to serve us “faithfully”, it is necessary that it remain undamaged for as long as possible. To do this, first of all, you need to have wooden or Teflon special spatulas in your household for turning or mixing the prepared food. Also, do not put an empty pot or pan on the fire.
By the way, experts advise purchasing dishes with a thick bottom, since experience shows that thin pans, no matter how carefully you take care of them, for some reason do not last long.
And now some tips about dishes made from various materials. I hope they will be useful to housewives.
In order for any porcelain tableware to serve longer, it must be “hardened”. Cups, saucers, plates, etc. are filled with cold water for several hours. And then, taking out one item at a time, they douse it with hot water.
Enamel dishes are also “hardened”, but in a different way. A new pan is filled to the brim with salt solution: 2 tbsp. l. per liter of water and let it boil. Then leave until cool.
But it is better to take care of even “hardened” enamel cookware and not place it directly from the refrigerator on a hot stove - a sharp temperature change can cause the enamel to crack.
And one more thing. It turns out that white enamel slows down the absorption of heat, which means it will take you longer to cook in such a pan than in a pan with dark enamel.
By the way, experts consider enamel or stainless steel containers to be the best for making jam.
Teflon is a good, but, unfortunately, very fragile non-stick coating. Therefore, to wash such dishes, you should not use not only metal scourers, but also powdered detergents - even they can scratch the Teflon. Wash pans and pots with a soft washcloth and liquid detergent, and then dry thoroughly with a towel.
Not only heat-resistant glassware is suitable for the microwave oven. You can use other glass, if, of course, there is no lead in it. And also porcelain - only it should not have metal patterns, including “golden” borders.” Clay dishes are also suitable - if they are glazed over the entire surface (including the bottom). But when using plastic, be careful - carefully read the instructions of the company that manufactured the dishes.
Better yet, avoid using microwave ovens at all, since they are also very harmful to health if used constantly. But since now we are talking about harmful dishes, the dangers of microwaves will be discussed in another article.
How to remove heavy metals from the body
The body, in essence, is capable of removing waste and toxins without external intervention. However, working and living in harmful conditions, leading an unhealthy lifestyle, we accumulate an excess of toxic substances, which our body can withstand with great difficulty. Heavy metals can accumulate in the plants and animals we eat. They can get into us with air, water, exhaust gases, tobacco smoke, household chemicals and harmful utensils (copper, lead, iron). Isotopes of heavy metals settle on internal organs, causing various diseases.
Eat foods containing pectin. Pectin has the beneficial property of collecting heavy metal salts on its surface. It is found in vegetables, fruits, and berries. A product such as beets, for example, also contains flavonoids, which convert heavy metals into inert compounds. The starch of potatoes, boiled in their skins, absorbs toxins from the body, removing them naturally. Carrots, pumpkin, eggplant, radishes, and tomatoes also remove heavy metals.
Eating apples, citrus fruits, quinces, pears, apricots, and grapes helps eliminate toxic substances. The berries of rowan, viburnum, raspberry, blueberry, and cranberry bind heavy metals into insoluble complexes, which are subsequently easily eliminated by the body. By eating lingonberries, blueberries, blackberries, cloudberries and sloe, you cleanse your body of accumulated toxic substances. It is even beneficial to eat marmalade made from these berries.
Drink tea made from chamomile, calendula, sea buckthorn, and rose hips. Tea made from these herbs protects cells from the penetration of heavy metals and promotes their elimination. Rosehip and sea buckthorn oils are also useful for heavy metal poisoning. Remove radioactive cesium isotopes from the body using sorrel, spinach, and salads.
Take substances containing lignan, it neutralizes radionuclides. Such substances are found in plants: juniper, sesame and burdock seeds, in the roots of lemongrass and eleutherococcus. Also, with constant exposure to isotopes of radioactive metals, it is recommended to use 40 drops of tincture of aralia, leuzea, Rhodiola rosea, and ginseng before meals.
Drink tea made from the herb coriander (cilantro), it can remove mercury from the body within two months. Brew four tablespoons of chopped cilantro with a liter of boiling water in a non-metallic container and drink after 20 minutes.
Carry out rice cleansing procedures. They are especially recommended for people employed in hazardous work. Rice removes toxic metal salts from the body. Soak a spoonful of rice in water in the evening, cook it without salt in the morning and eat it.
Use oat decoction to cleanse heavy metal salts. Fill a glass of oats with two liters of water and boil over low heat for 40 minutes. Drink half a glass four times a day, this will cleanse you of heavy metal salts, including cadmium, which is found in tobacco smoke.
Take care of yourself and your family! Be healthy! published econet.ru
Types of glass
Quartz glass
Quartz glass is produced by melting high-purity silica raw materials. Quartz glass consists of silicon dioxide SiO 2 and is the most heat resistant glass: its linear expansion coefficient in the range 0 - 1000 °C is only 6x10 -7. Therefore, hot quartz glass, lowered into cold water, does not crack.
The softening temperature of quartz glass at which a dynamic viscosity of 10 7 Poise (10 Pachs) is achieved is equal to 1250 °C. In the absence of significant pressure drops, quartz products can be used up to this temperature. Complete melting of quartz glass, when products can be made from it, occurs at 1500-1600 °C.
Known two varieties quartz glass: transparent quartz and milky matte. The turbidity of the latter is caused by the abundance of tiny air bubbles, which cannot be removed when melting glass due to the high viscosity of the melt. Products made from cloudy quartz glass have almost the same properties as products from clear quartz, with the exception of optical properties and greater gas permeability.
The surface of quartz glass has a slight adsorption ability to various gases and moisture, but has the highest gas permeability among all glasses at elevated temperatures. For example, through a quartz tube with walls 1 mm thick and a surface of 100 cm 2 at 750 ° C, 0.1 cm 3 H 2 penetrates in one hour if the pressure difference is 1 atm (0.1 MPa).
Quartz glass should be carefully protected from any contamination, even such as greasy hand marks. Before heating the quartz glass, any opaque stains on it are removed with dilute hydrofluoric acid, and fatty stains with ethanol or acetone.
Quartz glass stable in all acids, except HF and H 3 PO 4. It is not affected by C1 2 and HCl up to 1200 °C, or dry F 2 up to 250 °C. Neutral aqueous solutions of NaF and SiF 4 destroy quartz glass when heated. It is completely unsuitable for working with aqueous solutions and melts of alkali metal hydroxides.
Quartz glass retains its electrical insulating properties at high temperatures. Its electrical resistivity at 1000 °C is 10 6 Ohm cm.
Regular glass
Common glasses include soda-lime, lime-potassium, and soda-lime-potassium.
Lime-sodium ( soda), or sodium-calcium-magnesium-silicate glass, is used to produce window glass, glass containers, and tableware.
Lime-potassium ( potash), or potassium-calcium-magnesium-silicate glass, has higher heat resistance, increased gloss and transparency; used to produce high quality tableware.
Lime-sodium-potassium ( soda-potash), or sodium-potassium-calcium-magnesium-silicate glass, has increased chemical resistance due to the mixture of sodium and potassium oxides; most common in tableware production.
Borosilicate glass
Glasses with a high content of SiO 2, low content of alkali metal and significant content of boron oxide B 2 O 3 are called borosilicate. Boric anhydride acts as a flux for silica, so that the alkali metal content of the charge can be sharply reduced without raising the melting temperature excessively. In 1915 the company Corning Glass Works began producing the first borosilicate glasses under the trade name Pyrex. Glass brand Pyrex is borosilicate glass containing at least 80% SiO 2, 12-13% B 2 O 3, 3-4% Na 2 O and 1-2% Al 2 O 3. It is known by different names: Corning(USA), Duran 50, Jenskoe glass G 2 0 (Germany), Gizil, Monex(England), TS(Russia), Sovirel(France), Simaks(Czech Republic).
Depending on the specific composition, the thermal shock resistance of such glasses is 2-5 times higher than that of lime or lead glass; they are usually much superior to other glasses in chemical resistance and have properties useful for electrical applications.
The softening temperature of Pyrex glass to a dynamic viscosity of 10 11 poise (10 10 Pas) is 580-590 °C. Nevertheless, glass is suitable for work at temperatures up to 800 ° C, but without excess pressure. When using a vacuum, the temperature of Pyrex glass products should not be raised above 650 °C. Unlike quartz glass, Pyrex glass is practically impenetrable to H2, He, O2 and N2 up to 600 °C. Hydrofluoric and heated phosphoric acids, as well as aqueous solutions (even 5%) of KOH and NaOH, and especially their melts, destroy Pyrex glass.
Crystal glass
Crystal glass (crystal) is high-grade glass that has a special shine and the ability to strongly refract light. There are lead-containing and lead-free crystal glasses.
Lead-containing crystal glasses— lead-potassium glass, produced with the addition of oxides of lead, boron and zinc. Characterized by increased weight, beautiful play of light, melodious sound when struck; used for the production of high-quality tableware and decorative items. The greatest use is for crystal containing from 18 to 24% lead oxides and 14-16.5% potassium oxide (light).
Lead-free crystal glasses include barite, lanthanum, etc.
Barite glass contains an increased amount of barium oxide. It has better gloss, higher light refraction and specific gravity compared to conventional glasses, and is used as optical And special glass.
Lantana glass contains lanthanum oxide La 2 O 3 and lanthanides (compounds of lanthanum with aluminum, copper, etc.). La 2 O 3 increases light refraction. It is of high quality; applied as optical.
Properties of glass
Density glass depends on its chemical composition. Density is the ratio of the mass of glass at a given temperature to its volume, depends on the composition of the glass (the higher the content of heavy metals, the denser the glass), on the nature of the heat treatment and ranges from 2 to 6 (g/cm3). Density is a constant value; knowing it, you can judge the composition of the glass. Has the lowest density quartz glass - from 2 to 2.1 (g/cm 3), borosilicate glass has a density of 2.23 g/cm 3 , the highest is optical glass with a high content of lead oxides - up to 6 (g/cm 3). Density lime-sodium glass is about 2.5 g/cm 3 , crystal- 3 (g/cm 3) and higher. The tabulated value for glass density is the range from 2.4 to 2.8 g/cm 3 .
Strength. Strength is the ability of a material to resist internal stresses resulting from external loads. Strength is characterized by tensile strength. The compressive strength for various types of glass ranges from 50 to 200 kgf/mm 2. The strength of glass is influenced by its chemical composition. Thus, the oxides CaO and B 2 O 3 significantly increase strength, PbO and Al 2 O 3 to a lesser extent, MgO, ZnO and Fe 2 O 3 almost do not change it. Of the mechanical properties of glass, tensile strength is one of the most important. This is explained by the fact that glass works worse in tension than in compression. Typically, the tensile strength of glass is 3.5-10 kgf/mm 2, i.e. 15-20 times less than the compressive strength. The chemical composition affects the tensile strength of glass in much the same way as it affects the compressive strength.
Hardness glass, like many other properties, depends on impurities. On the Mohs scale, it is 6-7 units, which is between the hardness of apatite and quartz. The hardness of different types of glass depends on its chemical composition. Glass with a high silica content has the greatest hardness - quartz And borosilicate. An increase in the content of alkali oxides and lead oxides reduces hardness; Lead crystal has the least hardness.
Fragility- the property of glass to collapse under the influence of an impact load without plastic deformation. The impact resistance of glass depends not only on its thickness, but also on the shape of the product; flat-shaped products are least resistant to impact. To increase the impact strength, oxides of magnesium, aluminum and boric anhydride are introduced into the glass composition. The heterogeneity of the glass mass and the presence of defects (stones, crystallization, and others) sharply increase fragility. The resistance of glass to impact increases when it is annealed. In the region of relatively low temperatures (below the melting point), glass is destroyed by mechanical stress without noticeable plastic deformation and, thus, is an ideally brittle material (along with diamond and quartz). This property can be reflected by specific impact strength. As in previous cases, changing the chemical composition makes it possible to regulate this property: for example, the introduction of bromine almost doubles the impact strength. For silicate glasses, the impact strength is from 1.5 to 2 kN/m, which is 100 times lower than that of iron. The fragility of glass is affected by the uniformity, configuration and thickness of the products: the fewer foreign inclusions in the glass, the more homogeneous it is, the higher its fragility. The fragility of glass is practically independent of its composition. With an increase in the glass composition of B 2 O 3 , SiO 2 , Al 2 O 3 , ZrO 2 , and MgO, the fragility decreases slightly.
Transparency- one of the most important optical properties of glass. It is determined by the ratio of the number of rays passing through the glass to the total luminous flux. Depends on the composition of the glass, its surface treatment, thickness and other indicators. In the presence of iron oxide impurities, transparency decreases.
Heat resistance glass is characterized by its ability to withstand sudden changes in temperature without breaking and is an important indicator of glass quality. Depends on thermal conductivity, coefficient of thermal expansion and glass thickness, shape and size of the product, surface treatment, glass composition, defects. The higher the thermal conductivity and the lower the coefficient of thermal expansion and heat capacity of the glass, the higher the thermal resistance. Thick-walled glass is less heat-resistant than thin-walled glass. The most heat-resistant glass is with a high content of silica, titanium and boron. Glass with a high content of sodium, calcium and lead oxides has low heat resistance. Crystal Less heat resistant than regular glass. Heat resistance ordinary glass fluctuates between 90-250 °C, and quartz: 800—1000°C. Annealing in special furnaces increases heat resistance by 2.5-3 times.
Thermal conductivity- this is the ability of a material, in this case glass, to conduct heat without moving the substance of this material. Glass has a thermal conductivity coefficient of 1-1.15 W/mK.
Thermal expansion is an increase in the linear dimensions of a body when it is heated. The coefficient of linear thermal expansion of glass ranges from 5·10 -7 to 200·10 -7. Quartz glass has the lowest coefficient of linear expansion - 5.8·10 -7. The thermal expansion coefficient of glass largely depends on its chemical composition. The thermal expansion of glass is most strongly influenced by alkali oxides: the higher their content in the glass, the greater the coefficient of thermal expansion. Refractory oxides such as SiO 2, Al 2 O 3, MgO, as well as B 2 O 3, as a rule, reduce the coefficient of thermal expansion.
Elasticity is the ability of a body to return to its original shape after removing the forces that caused the deformation of the body.
Elasticity is characterized by the elastic modulus. The elastic modulus is a value equal to the ratio of stress to the elastic relative deformation caused by it. A distinction is made between the modulus of elasticity under axial tension and compression (Young's modulus, or modulus of normal elasticity) and the shear modulus, which characterizes the resistance of a body to shear or chipping and is equal to the ratio of the shear stress to the shear angle.
Depending on the chemical composition, the normal elastic modulus of glass ranges from 4.8x10 4 ...8.3x10 4, the shear modulus is 2x10 4 -4.5x10 4 MPa. Quartz glass has an elastic modulus of 71.4x10 3 MPa. The elastic and shear moduli increase slightly when replacing SiO 2 with CaO, B 2 O 3, Al 2 O 3, MgO, BaO, ZnO, PbO.
Properties of Corning glass
| Glass code | 0080 | 7740 | 7800 | 7913 | 0211 | |
|---|---|---|---|---|---|---|
| Type | Silicate | Boro-silicate | Boro-silicate | 96% Silicate | Zinc-titanium | |
| Color | Transparent | Transparent | Transparent | Transparent | Transparent | |
| Thermal expansion (multiply by 10-7 cm/cm/°C) | 0-300 °C | 93,5 | 32,5 | 55 | 7,5 | 73,8 |
| 25 °C, up to temp. hardening | 105 | 35 | 53 | 5,52 | - | |
| Upper limit operating temp. for annealed glass (for mechanical properties) | Normal operation, °С | 110 | 230 | 200 | 900 | - |
| Extreme operation, °С | 460 | 490 | 460 | 1200 | - | |
| Upper limit operating temp. for tempered glass (for mechanical properties) | Normal Operation, °C | 220 | 260 | - | - | - |
| Extreme operation, °С | 250 | 290 | - | - | - | |
| 6.4 mm thick, °C | 50 | 130 | - | - | - | |
| 12.7 mm thick, °C | 35 | 90 | - | - | - | |
| Heat resistance, °C | 16 | 54 | 33 | 220 | - | |
| Density, g/cm3 | 2,47 | 2,23 | 2,34 | 2,18 | 2,57 | |
| Optical voltage sensitivity coefficient, (nm/cm)/(kg/mm2) | 277 | 394 | 319 | - | 361 |
